Follow-up control system



Jan. 28, 1947.

E.. F. W. ALEXAND'ERSON FOLLOW-UP CONTROL SYSTEM 3 Sheets-Sheet 1 Fileds'ept. 21, 1935 i l a Inventor: Ernst. F WAlexanders on @y if .9 A

His 'ttorneg Jam 28, 1947- E. F. w. ALExANDERsoN 2,414,919

FOLLOW-UP CONTROL SYSTEM Filed Sept. 2.1, 1935 3 Sheets-Sheet 2 Fig.;

Inventor:

r9 is ttornepg.

Ernst FW Alexandersorm *Jaunl 28, 1947. E; F. w. ALExANDERsoN 2,414,919

FOLLOW-UP CONTROL SYSTEM Filed Sept. 21. 1935 3 Sheets-Sheet 3 auK4Inventor: Ernst Fi VV. AI exandeT-son,

H i s ternes.

' Patented .1.111.128,1941' UNITED s'ni'l'izsA PAT-awr OFFICE FOLLOW-UrCONTROL SYSTEM Ernst F. W. Alexanderson,

signor to General Electric Company, a corporation of New YorkSchenectady, N. Y., u-

ApplicationvSeptember 2l, 1935, Serial No. 41,580

l This invention relates to control systems, more particularly to theclass ofcontrol system known as follow-up control systems, in which aremote object is driven into correspondence with a pilot device, and anobject of the invention is the provision of a simple, reliable,eiiicient, and improved control system of this character.

If a heavy or massive object, such 'as' a naval gun, is to be driven in'correspondence with the movement, of a light pilot device, such as amanually movable sighting telescope, the control system is generallyreferred to as a, torque ampli-v fying system, because a much greatertorque is required to move the object than is required to move the pilotdevice. In systems of this character, means are provided for driving thedriven 16 Claims. (Cl. 172-239) v lll mitting device actuated by thepilot device and x an electrical receiving device connected to thedriving means, together with connections betweenthe two devices foractuating the .power control in accordance with the positionaldisagreement -.of the pilot device and driven object. A diiferentialdevice is included in these connections and means for measuring thevelocity of the pilot device are provided for actuating thisvdifferential device to act upon the power control so as to cause thedriving means to advance the driven object an amount equal to that by'which' the driven object would otherwise have to lag the pilot devicein order to cause the driven object to move at the same velocity as thepilot device.

Another aspect of the invention relates to follow-up systems in whichthe driving power for the driven object is supplied through a fluid l0pressure variable 'speed transmission device whose operatingcharacteristics tend to 'produce instability and oscillations in thesystem. Ac-

cordingly, a further object of this invention is the provision of meansfor eliminating these un- 25 desirable characteristics in a systemutilizing such a predetermined 4number of revolutions of the controlshaft of a mechanical control valve. In either case, this full openingis brought about by the driven object lagging the pilot device by anangle which ina typical casemay also be assumed to be 1. Thus. for fullspeed, the error is 1. 'I'his error is referred to as the dynamicaccuracy. An opening of the power control of approximately 1 is usuallysufficient to move the driven object very slowly from onestaticpositio'n to another. This accuracy, which is referred to as.' thestatic accuracy of correspondence is sufficient. An'important object ofthis invention is 40 the provision of "means for bringing about adynamic accuracy equivalent to the static accuracy.

In carrying'the invention into eect in one a transmission device sothat' the `system will have the desired stability and accuracy. f Inillustrating the invention in one form thereof, it is shown as embodiedin a control system for causing a gun to reproduce the movements andpositions of a sighting telescope, but it will be understood of coursethat the control system has other industrial applications.

For a better and more complete understanda5 ing of the inventionreference should now be' had formv thereof, the pilot'device and drivenobject t@ acts differentially to control the driving means to drive thedriven object toward correspondence with the pilot device at a velocityproportional to the positional disagreement between the pilot device anddriven object, and means responsive to the velocity of the pilot deviceare provided for controlling the driving means to advance the positionof the driven object an amount proportional to the velocity. ,A specificembodiment of the invention utilizes an electrical trans# to thefollowing specification and to the accompanying drawings in which Fig. 1is a simple, diagrammatical illustration of an embodiment Oi theinvention; Fig. 2 is a detail utilized in a modification of Fig. 1; Fig.3 is a simple schematic diagrammatical,illustration of a modification ofthe modification of Fig. 1; Fig. 4 is a modification of Fig. 3 and Fig.5 is a diagrammatical representatlon of the modication of the system ofFig. 1.

Referring now to the drawings, an object such as a gun I0, is rotated intrain under the control Of a control or pilot devicerepresented by thetelescope iI. The gun I0 is driven by any suitable driving means, suchfor example as the direct `current electric motor I2 to whose drive`shaft, the gun mounting platform is connected by suitable reductiongearing I3, I 4. Direct current is supplied to the varmature of thismotor by any suitable means, such for example as the electric termediatez supply transformer I9 and whose other terminal tially 180 out of phasewith the valve apparatus I illustrated as comprisinga pair of electricvalves I8 for supplying current in `one direction to the amature of themotor I2 and a second pair of valves I1 for supplying direct current tothe amature inthe reverse direction. The electric valves are in turnsupplied froml a suitable source of alternating voltage, representedd bythe supply lines I3. through a suitable supply transformer I9, theprimary winding of which is connected to the middle and upper supplylines and the secondary windings of which are connected to the anodes ofthe four valves as illustrated. The direct current motor I2 is providedwith a separately excited field winding 20 which is supplied from anysuitable separate source of direct current such as that represented bythe plus and minus signs.

Although the electric rvalves may be of anyV suitable type, they arepreferably of the three electrode type having a small quantity of anincrt' gas introduced into the envelope after exhaust. This inert gasmay be mercury vapor or i any other suitable gas and it serves to changethereby constituting the valve a grid controlled l arc rectifier.

The average value of the current flowing in the anode circuit ofelectric valves of this characdetermined amount, usually more than 90,the

current flowing in the anode circuit is a minimum or substantially zero.-For intermediate phase reiationships, the current flow hascorresponding intermediate values.

Alternating voltage is supplied tothe gridsof the electric valves IB andI1 by means of grid transformers 2I and 22, respectively, the primarywindings of which are connected in series relationship with thesecondary winding of a grid 5 biasing transformer 23, one of theterminals of whose primary winding is connected to an intap of theprimary winding of the is connected to the lower supply line IB. Thisconnection of the primary winding of the biasing transformer serves toderive a voltage for the grid or input circuit of the electric valvewhich 1 is .more than 90 lagging with respect to the anode voltagesothat both pairs of valves are held at cut off and de-energizedl andsupply no current to the armature of the motor I2.

For the purpose of varying this phase relation.

ship of the grid and anode voltages, a component voltage is supplied tothe grid or input circuit so through a transformer, one terminal of thesec' ondary winding. of which is connected to the common point betweenthe primary windings of the grid transformers 2l and 22 and the oppositeterminal of which isI connected to anintermediate point of the secondarywinding'of the bias ltransformer 23. This component voltage issubstantially in phase with the anode voltage of one pair of. valvesand, therefore. of course, substanof the other pair of valves. Thus, itwill be seen that by varying the magnitude of this component voltage,the phase relationship of the resultant grid voltage, i. e., vthevectoral sum of the l the usual electronic discharge into an arc stream,

nitude ofthe current supplied to the electric` motor is correspondinglyvaried. v It will also be seen, that by reversing the polarity of thiscomponent voltage and varying its magnitude, opposite pair of valveswill be energized and caused tosupply a current to the electric motorhaving a value dependent upon the magnitude of the component voltage.For the purpose of varying the magnitude of the component voltagesupplied to the grid circuit of tne electric valve apparatus, suitablerotary induction apparatus actuated differentially by the telescope IIand the gun I0 is provided. This rotary induction apparatus comprisestwo electrical transmitting devices 25 and 28 and two electricalreceiving devices 21 and 28.

The transmitting device 25 comprises a rotor member provided withA asingle circuit vwinding (not shown) and a stator member provided with adistributed poly-circuit winding (not shown) which 'is physicallysimilar to a three-phase winding. The single circuit rotor winding isconnected to the upper and middle supply lines I8. The transmittingdevice 28 is in all respects identical with the transmitting device 25and its single phase rotor winding is similarly connected to the top andmiddle supply lines I8. Asindicated.' the receiving device 29 is inailrespects identical with the transmitting devices 25 and -2B. However,the rotor winding ofthe receiving device is connected to theprimary-'winding of the transformen and' the terminals of the statorwinding are connected by means of conductors 29 to correspondingterminals of the .stator winding of the transmitting device 2B.

The single circuit winding of thetransmitter 26, when energized,produces an alternating magnetic eld by means of which a voltage isinduced in the stator winding. therebycausing a current to flow in thestator winding of the receiver 23. 'Ihis current in turn produces' analternating magnetic eld by means of which a voltage is induced in the.rotor winding of the of the rotor winding and the axis of the magneticfield is otherthan 90. Therefore, when this 90 relationship obtains, novoltage is induced in the rotor winding and consequently no componentvoltage is supplied to the grid circuit rotor member of the receivingdevice 21 and t .ugh gearing 3l, 32 to the shaft of an electric motor33. 'I'his motor 33 is a direct current motor similar to the motor I2and is supplied with direct current from. a. suitable source vconventionally represented by electric valve apparatus 34 which is inall respects identical with the electric valve apparatus I5. The rotorwinding of the receiving device 21 is connected to the grid or inputcircuit 'of the electric valve apparatus 34 and the terminals of thestator winding are connected by means of connections 3l `to anodevoltage 7o corresponding terminals of the stator winding of thetransmitter 25.

From the foregoing, it will be seen that the transmitting devices 25,28,the receiving devic'es 21, 23 and the electrical connections 29, 35concomponent voltage and the grid bias voltage 25'stitute connectionsbetween the sighting telescope the' receiver when the relationshipbetween the axis is' interposed.

andere i, :5 II and the driving motor I2; Andit-willalsobe seen that thedinerential device 3l isintcrposed in these connections. `As shown, thisdiIi'erential device comprises an input gear 3l. connected throughgearing 3I, 32 to the shaft of motor 33,

an output gear 30s connected Ato the rotor shaft of the transmitter 26and a third element 30s carrying a pair ot planetary pinions meshingwith ies in magnitude. in proportion to the angle by which the-rotor Vofthe receiver v23 lags the rotor of the transmitter 26, or in other wordsby an amount proportionalto the angle of lag between input and outputgears 3ll and 36s.- The third element of the dinerential device isactuated in one direction or the other by suitable means illustrated asa ilexible metal bellows 36 to which it is connected by means of agear31. These bellows in turn are actuated by uid pressure supvin adirection corresponding to the direction s which the telescope -II ismoved.

plied from asuitable means illustrated as an oil pump"'33. 'Althoughthis pump may be of any suitable type, it is preferably a positivedisplacement, gear type. pump provided with a'suitable by-passing system36 in which a by-pss valve lll The rotor of the pump 36 is connectedthrough l gearing II, 3|, 32 to the shaft of the motor 33 and ,r theby-Dess valve 46 is so adjusted that the iluid ypressure developed bythe pump is substantially proportional to the velocity, i. e., therotation of the motor 33.

4With the above understanding of the apparatus 'and its organization inthe completed system, the

operation of the system itself will readily be un- .derstood from thefollowingvdetailed description:

Rotation of the telescopev II produces a corresponding rotation o theaxis of the magnetic eld of the stator win l of theV receiving device21. As a result of this change in the position of the magnetic ileld, avoltage is induced in the'rotor winding of the receiver which issupplied as a component voltage to the grd"circuit of the'electricvvalveapparatus 3l, thereby energizing the electric valve apparatus andcausing it to supply current to the electric motor 33 for rotation l,inthe direction corresponding to the direction of rotation-:of thetelescope II. Since the rotor member vofthe' receiver 21'is connectedthrough gearing 1ML/3,2 to the motor 33, the rotor member of thereceiver isvlikewise rotated in a direction corresponding to thedirection oi! rotation of the the driven object Il and the pilot deviceII. As this component voltage increases, it advances the phase oi thegrid voltage 'of one of the pairs of ,valves I3, I'I with `respect, tothe anode voltage and causes this pair oi' valves to supplya directcurrent to the armature o! the motor I2 in such a direction thatthelmotor I2 drives the gun I3 1f the te1eseope is being movedst a speedequivalent to the maximum speed at which the motor I2 can drive the gun'I0, it will be clear-Lthat thevrotor member 'of `the receiver 2l mustlag the rotor member of the transmitter 26 by the amount v necessary toproduce a component voltage sutilcient tocause the electric valveapparatus to supply the'amount of current required to drive the motor I2at maximum speed. For lesser speeds,

the component voltage required is correspondingly less and therefore,the rotor of the receiver 28 Will lag the rotor of the transmitter 26 bya correspondingly smaller angle. It will, therefore, he

seen that the component voltage required to energize -the electric valveapparatus to drive the gun I6 at any velocity is proportional to thatvelocity and that the rotor of the receiver 28 must therefore lag therotor of the transmitter 26 by an angle proportional to the velocity.And it will also be seen that in the absence of the provision of anyspecial means for preventing it, the gun III must lag the telescope IIby an angle proportional to the velocity ofthe telescope. As pre-'-viously pointed out, this would be undesirable and is prevented byadvancing the rotor of the interr mediate transmitter 26 an angleproportional to telescope. If the telescope is stopped, the motor 33will nnally drive the rotor member of-the receiver to a position suchthat the axis of the rotor winding is at right angles to the magneticfield of the stator winding with the result that the component voltageis reduced to zero, the electric valve apparatus 34- is deenergized andthe motor v 33 is stopped. i

.This rotation oi'the motor 33 also drives the rotor member ci thetransmitter 26. Since the third element 30s of the differential is heldat rest by the bellows 36 when the motor 33 begins to f rotate, therotor of the transmitter 26 is rotated ing of the receiving device 28 isrotated a corresponding amount and as a result, a voltage is induced inthe rotor winding o! thelreceiver 28 and is supplled'as a componentvoltage through the valve apparatus I5.l This component voltage varthevelocity of the telescope II. Since the motor 33 is driven at a speedwhich is substantially proportional to the speed of the telescope II,the oil pump 38 which is driven by the motor 33, produces a pressuresubstantially proportional to the speed oi the telescope, and thispressure is applied to the bellows 36, which respond to rotate lthe Sear3l andthe gear 36e of the differential device an amount proportional tothe pressure and also proportional to the velocity of the telescope I l.Rotation of the gear 36e produces a rotation of the rotor of thetransmitter 26. 'The connections of the bellows to the oil pump are sochosen that the rotationof the rotor of the transmitter 26 is in thesame direction as that in which the rotor'was driven by the motor 33. Inother words, the position of the rotor of the transmitter 36 is advancedby an angle proportional to the velocity of the telescope II. Thisadvance in the position of the rotor of the transmitter momentarilyincreases the component voltage supplied to the grid circuit of theelectric valve apparatus thereby causing an increased current to besupplied to the motor I2. As a result, the speed of the motor I2 isslightly increased momentarily so as to advance the position of the gunIii with respect to the position of the telescope II. Owing to itsincreased speed, the gun l I6 begins to overtake the transmitter 26,theretransformer. to the grid circuit of the electric by lessening theangle between the transmitter 26 and receiver 2t. After this angle hasbeen diminished to its former value and the advancing movement -of thetransmitter 26 has been completed, the gun I0 will again be moving atthe speed at which the rotor of the transmitter 26 is being rotated. Therotor of the receiver 28 and transmitter 2B by an angle proportional tothe velocity. but since the rotor of' the transmitter 26 'is in advance.of the telescope ll by an angle corresponding tothe velocity of thetelescope, the gun I will be in correspondence scope I I. It will,therefore, be seen that the gun I0 will be in correspondence with thetelescope Il both when the system is at rest or when in movement at. anyconstant` speed. In other words, the dynamic accuracy has been madeequal 'to the static accuracy andthe velocity lag has been eliminated.

It has been pointed out that the motor 33 constitutes a speed responsivedevice. In other words, its speed is a measure -of the velocity of thetelescope Il. Itis also to be noted that the motor 33 measures thevelocity of the system at the-telescope and the driving means, whichpoint,

with the tele- 8 l motor t through a fluid pressure variableconventionally because it is a'well-knwn device sold upon the market andbecause its specific internal structure constitutes no part of thepresent invention. It is sufcient to understand that the shaft driven bythe motor 50 drives a variable stroke oil pump, which supplies a varil vable volume of oil to an oil motor which drives an intermediate point inthe connections between in the illustrated embodiment, is. the receiver21,-

and that the velocity correction is introduced at a subsequent pointinthe connections, namely, through the differential 30. The method ofmeasuring the velocity at one point in the connection and introducingthe correction at a subsequent point 1s an important feature of thisinvention,

because if the velocity correction were introduced at a point aheadofthe point of measurement, v

there would be a tendency for the measuring means to measure thecorrection as well as the error and thusi-to introduce oscillations andinstability into the system. l.

In the modication of Fig. 2, the bellows 3B of Fig. 1 are replaced by acylinder. 42 within which the output shaft 62. The amount of oilsupplied to the oil motor is controlled by means of a control shaft 53which, when rotated, varies the stroke of thel oil pump. When no oil issupplied to the oil motor, the output shaft B2 is at rest,

and when a maximum amount issupplied, the

shaft 52 rotates at a maximum speed.- Similarly, for intermediate ratesof supply, the shaft 52 rotates at'corresponding intermediate speeds.

The control shaft 63 is' actuated through difrerential gearing 54 by anvelectricmotor- Bl. Rotatlonvof the motor la rotates the input ele-vment of the .differential gearing and the controlV shaft 53 of thetransmissionl device 5I. As a result of the rotation of the controlshaft, the

output shaft 52 would continue to rotate indefinitely at a speedproportional to the -number of rotations of the input shaft l5. if itwere not for the fact that the output shaft is connected Iback throughgearing 56 and the diiferential device 54 to the control shaft so thatwhen the output shaft is rotated it turns the controlshaft a, movablepiston 43 is arranged. Suitable spring means 44 are provided forcentering the piston within the cylinder. The upper end of the cylindercommunicates with one port of the gear pump 45, which corresponds to thepump I8 of Fig.- l,

and the opposite end of the cylinder communicates with the v`oppositeport of the pump. .Each of' these ports may be either an intake port ora -discharge port, depending upon the direction of rotation o f thepump. The piston 43 is connected through a linkage 48 to a gear 41 whichcorrespends to the gear 31 of Fig. 1. When the pump 45 is at rest, thepiston 43 is in the central position ,in which it is shown and the gear41 occupies the same position that the gear 31 oi' Fig. 1 ocd cupieswhen the pump 38 is at rest.

The cperatmn of the System `of Fig. 2 is iden-t1.-

cal with that described for Fig. 1, with the ex A ception that thefunctionsperformed by the pump 3B and the bellows 46 are performed bythe pump` 4t. and the cylinder 42 and piston 43. In the event that thedisplacement of the piston is not as nearly proportional to the speed ofthe ,pump 4-5 as `is desired, the wall of the cylinder may beprovldedwith tapered slots 48 so that the bypassing effect is graduallyincreased as` the Diston` moves from its center position to either ,endof the cylinder. Thus, if the pump 46 should have a characteristic suchthat the pressure increases vfaster ,thanl the first power of the speed,the slots 48 can be shaped so that the fluid pressure and y thedisplacement of' they piston will be proportional to the speed of thepump;y The operation of this modification of the system is in all otherrespects identical with the foregoing description of the operation ofthe system of Fig. 1 and consequently a repetition of this operation isunnecessary. s

In the modification of Fig. 3, the driving power 'for the gun 4I issupplied by a suitable electric .ture and fimction with the transmittingdevice a backward toward its initial position. 'As the control shaft isturned backward, the speed of c the output shaft is diminished and whenthe control shaft is returned to its .initialposition, the output shaftis' stopped. -Thus ittwill bessen that with the differential gear. 54connecting the output shaft and the4 control shaft, the transmissiondevice Il functions inherently as a folit will lag the input shaft by anamount-proportional to the velocity of the output shaft. This amount isthe same amount that the control shaft B3- would have to be. rotated tocause the shaft 52 to rotate continuously at that speed if there were nodifferential follow-unconnection between the output. shaft and the inputshaft. 'I'his amount may be represented by an angle, and this angle,wwhich is proportional to the velocities of both the output shaft andthe input shaft, is known as the velocity lag.

The remainder of the modification of Fig. 3

is substantially identical with the .corresponding portion of the systemof Fig.l 1, with the exception that the mechanical differential device30 and the fluid pressure pump 33 of Fig. 1 are respectively replaced byan electrical differential device B1 and an electrical torque motor 5B.

. Briefly, the transmitting device 59, receiving device 60, .poweramplifier 0| and direct current motor 02 correspond and are identical instmo- 25, receiving device 21, power amplifier 34 and direct currentmotor 33, respectively, of Fig-1. Similarly, the elementsof the repeatersystem,

-that is to say, the transmitting device 8l, re-

ceiving device 84, and power amplifier are identical in structure andfunction with the speed Y .transmission device ll This device isillustrated previouslydescribed and diilers from them only in that itsrotor member is'provlded with a polycircuit distributed winding.Corresponding terminals of the stator windingof the transmitter 63 andthe differential device 51 are connected together by means ofconnections 66 and sim- 10 ilarly, terminals oi.' the rotor winding -oi?the differential device 5l are connected by means of conductors 51 to,corresponding terminals of the stator winding of the receiver 64. y Therotor winding of the transmitter 63 induces voltages 15 inthe statorwindings which in turn cause currents to iiow in the stator windings ofvthe differential device 51, thereby producing an alternating magneticfield which in turn induces voltages in the rotor winding of thedifferential device. These voltages cause currents to flow in the statorwinding of the receiver 64, which currents produce an alternatingmagnetic iield and l this magnetic field induces a voltage in the rotorwinding of the receiver except when the axis of the rotor winding isk atright angles with the axis of this magnetic eld. The system is den l.energized and at rest when the axis of the rotor winding of thereceiver. is perpendicular to the axis of the magnetic ileld of thestator winding because no component voltage is supplied to the gridcircuit of the electric valve apparatus 65 and therefore no current issuppliedA to the electric motor 55. If the rotor member oi' thestandstill, the position oi' the axis of the rotor lwinding is changedwith respect to the position of the axis of the magnetic iield of thestator 'Winding As aresult, the relationship of the 40 voltages inducedin the separatev coils oi' the rotoriwinding is changed and similarlythe rel'ationshin of the currents flowing in the separate coils of thestator winding of the receiver 6l is ceiver 84 and input shaft 53 areboth seared to motor 55, it will be clear that the gun 49 will tend v tolag receiver 64 and telescope 68 by an angle proportional to velocity.

As shown, spring means 69 are provided for opposing rotation of thearmature of the torque motor 58 so that it is free to rotate onlythrough a limited angle. The armature of this motor is connected to andsupplied from the same power amplier 56 as that from which the repeatermotor 52 is supplied and therefore, if its rotor were not blocked, itwould tend to rotate at a speed either equal to or proportional to thespeed of the motor 62, which as previously pointed out is proportionalto the velocity of the telescope 68. However, since the rotor of themotor 58 is prevented from rotating, its amature draws a current throughthe power amplifier 6I producing a torque proportional to the currentand, there,- fore, proportional to the velocity of the telescope. Thistorque rotates the rotor member of the electrical derential device 51,thereby varying the component voltage supplied to the power amplifier 65and causing the motor 55 to increase the speed of rotation of the inputshaft s and likewise the speed of the output shaft 52.` As aresult, thevelocity of the gun 59 is momentarily increased above the velocity ofthe telescope 58 and therefore tends to overtakeV the telescope.

At the same time. the motor 55 advances the rotor of the receiver dllwith respect to transmitter 63 and therefore with respect to telescope68. When the angle of advance of receiver 54 becomes i diierentialdevicel 5T is rotated a predetermined 35 y equal to the angle of advanceof the dierentia] amount when the remainder of the system is at `device5l, the control voltage supplied to the ampliiler 65 is decreased to itsformer value. As a result, the speed of the motor 55 is decreased to itsformer value and the motor continues to drive the rotor of receiver t5and'inp'ut shaft 55s at a velocity equal to that of the telescope, butin l advance of the position thereof by an angle equal to the angle ofadvance of dierentlal device 51;

in other words, an angle proportional to the velocity of the telescope.Since it is necessary for changed. This produces a shift of the axis .of457 the output Shaft 52 and gun 49 tolag the Pos1..

the magnetic tleld-oi' the receiver so that the rotor winding is nolonger perpendicular to the axis and consequently avoltage is induced in1 the rotor windings which is supplied as a component voltage to thegrid circuit voi' the power 50 amplier 65. ,-Thus, brieiiy, the resultof a ro tation of-the rotor member oi' the differential v device 51 isto produce a change in the component voltage supplied to the inputcircuit of the power amplifier 65. 55

In operation. the rotation of the sighting telef scope 68 energizes thepower amplifier 8| and causes the motor 62 to drive the transmitter 63of the repeating system at a velocity equal to 'the velocity of therotor of the transmitter 59 60 which is connected to the telescope`58.SimiA larly, this rotation of the transmitter 83 of the repeater systemenergizes the power amplifier 85 and causes the motor 55 to drive theinput shaft 55s of the variable speed transmission device 5| 65 at avelocity corresponding to the velocity of the telescope 68 which in turnresults in rotation of the output shaft 52 at a velocity correspondingto the velocity of the input shaft 53 and there- I fore proportional tothe velocity of the telescope 68. Since the motors 62 and 64 arelightlyloaded, the receiver .64 rotates in substantial correspondence withtransmitter 59 and telescope 58. But, as previously pointed out, theoutput shaft 52 and gun 49 will lag the input shaft 55s'by an angle 75tion of -the input shaft 55s by an angle propor. tional to-veloqity, thegun 69 will come into correspondence with the telescope at the instantthat the input shaft 55s reaches a position in advance the transmitter63 and likewise with respect to t position of the telescope 68, by anangle propo ional to the velocity of the telescope, the gun 49, althoughstill lagging the position of the ro-l tor of the receiver 64, by thissame angle continues in correspondence throughout the remainder of themovement of the telescope. Although this catching up or advancing actionis described as taking place in a sequence of operation, it will beunderstood that these operations take place almost instantaneously andare not readily apparent to the eye.

In some cases, the system of Fig. 3 may give rise to a. small residualerror which can be overcome by the corrective means illustrated in Fig.

4, in which means are'provided for an accurateI comparison of theposition of the gun 'III with the position of the telescope. In thismodification,

' the receiver i5 andere device 12 and the electrical dif- A ierentialdevice 13 are identical in structure and i `the stator nected tocorresponding stator terminals ofthe function with the corrpondingtransmitting decomparison of the posi- Thi's receiving device 'l5 isFig. 3. For the purpose previously described in .the\

o! 'the telescope, the receiving device-1B is geared of the receiver I2are contransmitter 8l which is actuated by the telescope 3 5.-Similarly, the stator terminals of the transmitter 8.3 are connected tocorresponding stator vterminals of the receiver Il, the rotor winding ofwhich is connected to and supplies a component voltage to the inputcircuit or a power amplifier B1 which is in all respects identical withthe power amplifier i5 of Fig. i. Power to drive the gun et is suppliedby an electric motor 89 through the stator winding of this receivingdevice are connected'by means of conductors Il to correspondingterminals of the stator transmitting device 12. The rotor winding of isconnected to and supplies a component voltage to the input circuit of apower amplier liwhich is in all respects identical with the poweramplier it of Fig. 1. As indicated, the output circuit 'it of this poweramplier is connected across a resistance is which is included in theamature circuit of the torque motor ifi. A time delay device illustratedas a small direct current motor dii having its armature connected acrossthe output circuit is provided for slightly delaying the correctiveaction.

In operatic if the gun 'iii is out of correspondence with the telescopeeven after the velocity correction has been introduced as set forth inthe foregOing description of the operation oi the system oi Fig. 3, avoltage will be introduced in the rotor winding of the receiver i5 andthis voltage will be supplied as acomponent voltage of the input circuitof the power ampliiier il, thereby energizing the amplier and causing itto supply a voltage across the resistance 19. This will have the effector varying the current flowing in the armature of the torque motor 18,causing the torque ofthe latter to vary and t0 rotate the rotor of thediierential device 18, the amount necessary to cause the driving meansfor the gun 'Ill to drive it into a position of accurate correspondencewith the telescope. It is to be noted. that in this modification thecorrection for the residual error is introduced ahead of the point atwhich the error wsly pointed out, this tends to introduce oscillationsand instabilities in the system. However, the armature of motor 80 drawsa comparatively heavy current. at the instant when the correction isinitiated and as the armature comes up to speed. its current diminishesrapidly as its. counter voltage increases. When the armature of themotor Il draws a comparativelyheavy current. the voltage across theresistance 19 is correspondingly small, but' as the counter voltage ofthe motor increases, the voltage across the resistance 18 likewiseincreases. The application of the corrective voltage is delayed and thedelaying action of the motor I0. therefore, seems to be very similar tothe delaying action of a dashpot in applying the correcting actiongradually land thereby preventing hunting. f

The operation of the modied system or Fig. 4 is otherwise identical withthe foregoing description of the operation of the system of Fig. 3 andwill, therefore, not be repeated.

In the modiilcationlof Fig. 5, the electrical ditlerential device 51 ofFig. 3 1s replacedby the mechanical differential device 8| which isincluded in the shaft connections between the ro.- tor of the receiverl! and the rotor of the transmitter I3 of the repeater system. Asindicated,

windingofthea fluid pressure variable speed transmissiondevice identicalwith the device 5I `previously described in connection with Fig-3.

When the telescope B5 is rotated. the receiver 82 follows this rotationand drives the transmitter 38 of the repeater through the differentialdevice 8i, which controls the variable transmission device t@ to drivethe gun 88 in the manner already described in connection with the systemof Fig. 3. As in these previously described modifications, the gun t@will tend to lag the position of the telescope 8E by an angleproportional to the velocity of the telescope. In' order to eliminatethis velocity error, a mechanical speed `xneasuringdevice el is providedfor measuring the velocity oi the telescope titi and introducing acorrection proportional to the velocity. Since mechanical velocitymeasuring devices are wellknown and obtainable on the market, the deviceel is shown conventionally in the drawings. It is provided with an inputshaft 92 which is rotated by the receiver S2 at a speed corresponding lto the velocity of the telescope t5 and the output shaft t8 is displacedan amount yproportional to the speed of the input shaft 92. Thedisplacement of the output shaft 93 actuates the third element of thediierential device BI to introduce correction in the connections betweenthe re`- Y ceiver 82 and the repeater transmitter 83 which is similarand equal to the correction introduced through the differential devicein the modiiication of Fig. l. Accordingly, a repetition of thedescription of the manner in which this correction is introduced isomitted. Itis pointed is measured. As previe out, however, that as inthe `systems Vof Figs. l and 3, the velocity is measured ahead of thepoint in the connections at which the correction is introduced. As aresult, no oscillations or instalio-bility are introduced into thesystem along with the correction.

The modification of Fig. 5 is in all other respects identical with thepreviously described opieration of the modification of Fig. 3.

Although in accordance with the provisions of o0 vention is not limitedthereto, since alterations the patent statutes.' this invention isdescribed as embodied in concrete form, it will be understood that theapparatus, elements, and their organization is merely illustrative andthat the inand modifications will readily suggest themselves to persons.skilled in the art without departing from the true 'spirit of thisinvention or from the scope of the annexed claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. Means for moving an object vin pomtional agreement with a pilotdevice comprising driving means for said object, said driving meanshaving 7 0 a control element, means for actuating said con- 76 ing atransmitting device actuated by said pilot trol element to control vsaiddriving means to drive said object toward correspondence with said pilotdevice in response topositional disagreement of said element and devicecompris- 'for' controlling said driving elle device, a re' ivingeviceconnected to said driving means; and connections' betweenA saidtransmitting and receiving devices, dierential means in saidconnections, means connected to' said diderential means and responsiveto velocity of i'or measuring the velocity-of said-pilot' device tingdevice connected to said pilot device, a'receiving device connected tosaid driving means receiving devices, differential me in saidconnections, and means for actuating said dinerential means to controlsaid driving meansto advance said object an amount proportional to thevelocity of said pilot device thereby to eliminate said positionaldisagreement.

3. A follow-up system comprising in combiand connecticm between saidtransmitting and nation a pilot device, a remote object, driving meansfor said object, means ior controlling said driving means to drive saidobject toward a position of correspondence with said pilot device at avelocity proportional to positional disagreement oi said pilot deviceand object comprising an electrical transmitting device connected tosaid pilot device, an electrical receiving device connected to saidobject and connections between said transmitting and receiving devices,diierential means included in said connections, and

means responsive to the velocity of saidpilot device for introducing acorrection throughfsaid differential means to cause said driving meansto advance the position of said object an amount; dependent upon saidvelocity thereby substantially to eliminate said positional disagreementwhile said pilot device is in motion.

4. A follow-up control system comprising a movable pilot device, a reoteobject, driving means for said object,`electrlc valve apparatussponsive to positional disa vice and object for energizing 4said valveappara.- tus to control said driving means to drive said object toward aposition of correspondence with -v said device comprising a transmittingdevice ac-` tuated by said pilotdevice. a receiving device connected tosaid" driving means and connections between sa'id transmitting andreceivingl devices, a diliferential .device included in saidconnections,` and means for actuating said differential means to causesaid valve apparatus to control said driving means to advance the.position o! said object an ainount proportional to' the velocity of saidpilot device' thereby to eliminate the velocity lag. I I

A follow-upsystem' comprising in combination a pilot device, a remoteobject, driving means for said object, means' responsivev to positionaldisagreement of said object and said device forv energizing said drivingmeans to drive said objecttowarda position of co1 respcndence with saidat a point lbetween said differential means and pilot device-andactuating said dinerential means to cause said driving means to advancethe position oi' said object an amount proportional to said velocity. s

6. A follow-up control system comprising a pilOt said object, controlmeans'for said driving means, means responsive to angular disagreementof said device and object for actuating said control means to energize.said driving means to drive said object into angular correspondence'with said pilot device 'comprising a transmitting device actuated bysaid pilot device, a receiving device connected to said driving meansand connections between said transmitting and receiving devices, .andmeans responsive transmitting device for introducing `an angular natesaid angular disagreement.

7. A follow-up contrei system object into positional agreement with apilot device comprising drivingmeans for said driven object, meansresponsive to positional disagreement o1 said object and device forenergizing said driving means to drivesaidobject toward positionalcorrespondence with said pilot device, an electric motor controlled bysaid pilot device and pump means driven by said motor for developing auid pressure in accordance with the velocityY of said device and meansresponsive to said fluid pressure for controlling said driving means toadvance said object an amount proportional to said velocity therebysubstantially to eliminatesaid positional disagreement.

8. Automatic synchronizing apparatus for .driving an object intopositional agreement with a pilot device comprising driving means forsaid' object, means ment of said device and object 'for energizing saiddriving means to drivev said object toward a position of correspondencewith said device comprising a receiving device'and connections betweensaid pilotdevice and receiving device,`

- devices, a mechanical connectionbetween said means, means re-"greement of said dedevice motor and said receiving device, a secondelectric motor -controlled by said pilot device and a differentialdevice included in 'said connections and actuated by said second motorfor controlling said driving means toladvance amount proportional tothevelocity oi'said pilot device therebyfsubstantially to eliminate saidangular disagreement. 9. A follow-up control system comprising a pilotdevice .a driven object, driving means for said object, mean'sresponsiveto angulardisagreement of said device and' object for controllingdsaiddriving means to drive said object tnwa comprising an electricaltransmitting device actuated by said device, 'an electrical receivingdevice connected to said driving means, and

tween said transmitting. and receivingdevices, a diierential device insaid connectlons, electric valve apparatus controlled by devicecomprising a transmitting device actuated f by said device, a receivingdevice connected to said driving means and connections between saidtransmitting and receiving devices, dinerential' ysaid pilot devic e andan electric motor controlled by said valve apparatus for actuating saiddinerential device to introduce an angular correction into Asaidconnections to cause said driving means "to advance said object anamount proportional to the velocity of said pilot device.

10. A follow-up control system comprising a device,v a remote object,driving means for to the' velocity-of said for driving an responsivetoposltional disagreesaid object :an

a position of correspondence with said pilot, device. a remote'obiect,driving toward a position means havtransmission-havins a conshaftand adifferential shaft and element for ingv a variable speed trol element,anl outputv connection between said stopping said transmission after anumber of,`

revolutions of t e output shaft dependent upon the operation of saidcontrol element, means responsive'to positional disagreement of saidpilot device and driven object for actuating said control element todrive said object toward a position of correspondence with said pilotdevice, and means for actuating said control element to, advance theposition of said object an amount proportional to the velocity of saidpilot device, thereby to eliminate said positional'disagreement.

l1. Automatic synchronizing' apparatus for driving an object intopositional correspondence with a pilot device comprising driving meansfor said object, means responsive to positional disagreement of saidobject and device for controlling said driving means to drive saidobject of correspondence with said device comprising an electricaltransmitting device "actuated by said device, an electricalreceivingdevice connected to said driving means, electrical connections betweensaid transmitting and receiving devices, and an electrical dierentialdevice included in said connections, and means for actuating saiddiierential device to control said driving means to advance the positionof said object an amount proportional to the velocity of said pil@1device, thereby substantially to eliminate s` d positional disagreement.

l2. .A control syste'm for causing a massive obl ject to reproduce themovement of a light pilot device comprising driving m is `for saidobject, means responsive to angular ,disagreement of said device andobject for controlling' said driving means to drive said object towardya position of correspondence. with said device comprising an electricaltransmitting device actuated by said control devicefan electricalreceiving device connected to said" driving means, and electricalconnections "between said transmitting and receiving devices, anelectrical differential device included in said connections, and anelectrical torque motor responsive to the speed .of said'pllot devicefor actuating said differential device to introvduce an angularcorrection proportional to the speed of said device thereby to controlsaid driving means to-advance the position of said object and eliminatesaid angular disagreement.

l3.'A follow-up control system comprising a pilot device, a. remoteobject, driving means for said object comprising a fluid pressureoperated variable speed transmission having an input corrtrol shaftv andan output shaft connected to said object, means responsive to angulardisagreement of said pilot device for controlling said driving means todrive said object toward correspondence with said pilot devicecomprising an electrical transmitting device actuated by said pilotdevice, lan electrical receiving device connected to said control shaftand electrical connections between said transmitting and receivingdevices, means for measuring the velocity of said pilot deviceat a.point between said drivingmeans and pilot device,` and means forintroducing an angular correction in the control between said measuringmeans and driving means to cause said .andere 16 means to advance theposition of said obamount proportional to the velocity` of drivin! lectan said pilot device.-

Y tric motor connectedto drive said .control shaft.'4

ing said shafts ,valve apparatus, and

'and means for measuring the velocity 14. A control system for moving amassive oblect in positional agreement with a pilot device comprising afluid pressure motor having an input control shaft and an output shaftconnected to said object and a differential device connectto provide forstopping said'output4 shaft after an amount oi' rotation proportionaltothe rotation of said input shaft, an elecelectric valve means forsupplying said motor, means responsive to angular disagreement of saidpilot device means to drive said object towardl correspondence with saidpilot device comprising an electrical transmitting device actuated bysaid pilot device.- 'an electrical receiving device driven by said motorand electrically connected to control said electrical connectionsbetween said transmitting and receiving devices, of said-pilot deviceand controlling said valve apparatus to advance the position of saidobject proportionally to the velocity of said pilot device.

l5. A follow-up control system comprising in combination, a pilotdevice, a remote object, driving means for said object comprising a uidpressure variable speed transmission device having an output shaftconnected to drive said object, an input control shaft and adifferential connecting said shafts for stopping said output vshaftafter an amount of rotation proportional to the rotation of said inputshaft, electric valve means and a motor supplied therefrom for actuatingsaid control shaft, means responsive to angular disv. agreement forcontrolling said 'driving means to drive said object towardcorrespondence with said pilot device comprising an electricaltransmitting device actuated by said pilot device, an electricalreceiving device connected to said motor for controlling said valveapparatus, and connections between said transmitting and receivingdevices, means in said connections for measuring the velocity of saidpilot device, and means controlled by said measuring means forintroducing a correction in said connections at a point between saiddriving means and point of measurement for controlling said valveapparatus 'to eliminate said angular disagreement.

16. Means for causing an' object to move in positional agreement with apilot device comprising driving means for said object, means responsiveto positional disagreement of said pilot device and object forcontrolling said driving means to drive said object towardcorrespondence with said device comprising an electrical transmittingdevice -connected to said pilot' device and an electrical receivingdevice connected to said object. means for advancing the positionof saidobject to eliminate said disagreement comprising a differential meansincluded in the connections between said pilot device and said object,and a torque motor whose torque is responsive to the velocity of saidpilot device for actuating an input member of said diilerential means anamount proportional to the velocity of saidpilot device.

ERNST E. W. 'ALExANDEasoN and object for controlling said driving

